Method for cleaning the upstream surface of a particulate filter

ABSTRACT

The invention concerns a method for cleaning the upstream surface ( 14 ) of a particulate filter ( 10 ) of a heat engine exhaust line, the filter ( 20 ) being arranged in a casing ( 12 ) having an outlet ( 22 ) for exhaust gases. The method comprises a step which consists in circulating a liquid flux through the particulate filter ( 10 ) from its downstream surface ( 18 ) towards its upstream surface ( 14 ) viewed from the direction of exhaust gas flow in the filter. The liquid flux circulated through the particulate filter ( 10 ) has a flow rate higher than 50 litres/minute and is distributed over the main part of the downstream surface ( 18 ) of the particulate filter.

FIELD OF THE INVENTION

The present invention relates to a method of cleaning the upstream faceof a particle filter of an engine exhaust pipe line, the filter beingdisposed in a casing having an outlet for the exhaust gases, the methodcomprising a step in which a cleaning stream is caused to flow backthrough the particle filter from its downstream face towards its facethat is upstream relative to the direction in which the exhaust gasesflow through the filter.

BACKGROUD OF THE INVENTION

Currently, in motor vehicles having combustion engines, and inparticular in vehicles having diesel engines, it is known that aparticle filter can be provided in the exhaust pipe line.

Such a particle filter is received inside a metal casing having an inletfor feeding in the exhaust gases and an outlet for removing the exhaustgases.

The particle filter is formed on a filter substrate such as siliconcarbonate. In the substrate, a succession of adjacent parallel channelsare defined, the channels being closed off at alternate ones of theirends. The gases thus flow through the side walls between adjacentchannels.

While the engine is operating, the particle filter retains sootparticles on its surface that is upstream relative to the direction inwhich the exhaust gases flow in the exhaust pipe line.

The soot particles gradually build up on the upstream face, therebyclogging the filter. In order to unclog the filter and in order toguarantee optimum engine operation, it is known that the filter can beregenerated at regular intervals. To this end, the soot on the upstreamface of the particle filter is burnt off. In order to facilitatecombustion of the soot on the particle filter, it is known that metaladditives can be added to the fuel with which the engine is fed, therebyenabling the combustion temperature of the soot to be lowered.

After the particle filter has been regenerated on successive occasions,a non-combustible residue builds up on the upstream face of the particlefilter. Such non-combustible residue is made up mainly of oxides, ofsulfates, and of phosphates of cerium, of zinc, and of calcium.

In order to conserve the performance of the engine, and to restore thefiltering capacity of the particle filter, it is necessary,periodically, to clean the particle filter mechanically.

To that end, it is known that the particle filter and its casing can bedismounted in order to clean the filter.

In one known method, a nozzle delivering a narrow jet of water (having asection of a few millimeters (mm)) is inserted into the casing facingthe surface of the particle filter which is downstream relative to thedirection in which the gases flow. Under control from automaticdisplacement means, the nozzle is displaced perpendicularly to thedownstream end surface of the particle filter, over a rosette patternpath in order to cover the entire surface of the filter.

That method requires the nozzle to be displaced over the entire surfaceof the filter. Such displacement can be difficult or impossible when thecasing of the particle filter has a converging segment at its outputthat has a profile that is made irregular because of the compactnessconstraints with which the casing must comply in order to be installedon the vehicle. In addition, the time required for cleaning the filteris very long because the nozzle must travel over the entire downstreamsurface of the particle filter.

OBJECT OF THE INVENTION

An object of the invention is to provide a method and a facility forcleaning a particle filter that does not suffer from the above-mentioneddrawbacks and that, in particular, enables the filter to be cleanedquickly and effectively.

SUMMARY OF THE INVENTION

To this end, the invention provides a method of cleaning the upstreamface of a particle filter of an engine exhaust pipe line, in whichmethod the cleaning stream that is caused to flow back through theparticle filter has a flow rate greater than 50 liters per minute(1/min), and is distributed over substantially all of the downstreamsurface of the particle filter.

In particular implementations of the method, said method has one or moreof the following characteristics:

the stream of liquid caused to flow through the particle filter has aflow rate lying in the range 200 l/min to 600 l/min;

the pressure of the liquid upstream from the downstream surface of theparticle filter lies in the range 5 bars to 50 bars, and preferably inthe range 15 bars to 25 bars;

the liquid has a temperature lying in the range 30° C. to 70° C.;

the liquid is water;

prior to said step in which a stream of liquid is caused to flow throughthe particle filter, said method further comprises a step in which theparticle filter is immersed in a bath subjected to ultrasound vibration;

after the step in which a stream of liquid is caused to flow through theparticle filter, the method further comprises a step in which a streamof gas is caused to flow through the particle filter, from itsdownstream surface towards its upstream surface;

during the step in which a stream of gas is caused to flow through theparticle filter, the stream of gas is distributed over substantially allof the downstream surface of the particle filter;

during the step in which a stream of gas is caused to flow through theparticle filter, the stream of gas has a flow rate greater than 3000l/min, and a static pressure greater than 2 bars;

said method comprises a succession of alternating steps in which astream of liquid is caused to flow through the particle filter and inwhich a stream of gas is caused to flow through the particle filter,from its downstream surface to its upstream surface;

the stream of liquid is fed into said casing via a duct connected to theoutlet via which the exhaust gases exit from the casing, and thecross-section of the duct is substantially equal to the cross-section ofthe exhaust gas outlet of the casing; and

during a portion of said step in which a stream of liquid is caused toflow through the particle filter, closure means are applied to on asmall portion of the upstream face of the particle filter.

The invention also provides a facility for cleaning the upstream face ofa particle filter of an engine exhaust pipe line, said facility beingcharacterized in that it comprises flow-generating means for causing astream of liquid having a flow rate greater than 50 l/min to flowthrough the particle filter, and in that said flow-generating means areadapted to distribute the stream of liquid over substantially all of thedownstream surface of the particle filter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on reading the followingdescription given merely by way of non-limiting example and withreference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of equipment for regenerating the soot onthe upstream face of a particle filter shown in section;

FIG. 2 is a diagrammatic view of a facility for cleaning the upstreamface of a particle filter shown in section, during a first cleaningstage; and

FIG. 3 is a view identical to FIG. 1 during a second cleaning stage.

DETAILED DESCRIPTION OF THE INVENTION

The figures show a motor vehicle particle filter 10 disposed inside ametal casing 12. The filter 10 and its casing 12 have been dismountedfrom the exhaust pipe line in which they are normally installed.

The particle filter 10 is constituted by a porous substrate in whichadjacent parallel channels are defined that are closed off at alternateends.

For example, the length of the particle filter 10 is 254 mm and itsdiameter is 144 mm. Its volume is 4.1 l for a mass of 3300 grams (g).

With such a filter, when it is clean, the back pressure measured for aflow speed equal to 12.7 meters per second (m/s) is 10 kilo pascals(kPa).

The numerical values given in the description below correspond to such afilter.

They are applicable for filters having characteristics adapted to treatan exhaust gas flow rate in the range 25 kilograms per hour (kg/h) to700 kg/h.

The particle filter 10 has a face 14 that is upstream relative to thenormal direction of flow of gas in the exhaust pipe line. The term“upstream face” 14 designates the upstream end surface of the filter andthe surfaces of the channels that open out in said surface. The upstreamface 14 of the particle filter is accessible through an open end 16 inthe casing 12. The open end 16 has a cross-section substantiallyidentical to the cross-section of the particle filter 14. When theparticle filter is mounted on an exhaust pipe line, the casing 12 isextended upstream from its end 16 by the casing of a catalyticconverter.

After prolonged use of the vehicle, the upstream face 14 of the particlefilter is loaded with non-combustible residue which must be removed fromthe filter during the cleaning operation. Furthermore, soot not burntduring a prior regeneration stage can also be present on the upstreamface of the filter.

The mass of ash, i.e. of non-combustible residue, on the upstream faceof the filter prior to cleaning is at least 100 g.

The filter 10 has a downstream face 18 opposite from its upstream face14, where “upstream” and “downstream” are terms relative to the normalflow direction of the exhaust gases in the exhaust pipe line.

Facing the downstream face 18 of the particle filter, the casing 12 hasa segment 19 converging from the downstream face 18 of the particlefilter to an outlet 20 normally serving to remove the exhaust gasescoming from the particle filter.

The outlet 20 has a cross-section corresponding substantially to thecross-section of the pipes making up the exhaust pipe line.

Before commencing the cleaning proper of the filter, consisting inremoving the non-combustible residue, the soot not burnt during a priorregeneration stage must be removed from the upstream surface 14 of thefilter after said filter has been dismounted.

For this purpose, the regeneration equipment shown in FIG. 1 is used.

The regeneration equipment comprises a tank 21 having an air intakeequipped with a fan 22. In addition, a burner 23 is disposed on one wallof the tank 21 in order to generate a flame inside the tank.

In the vicinity of the flame formed by the burner 23, an opening 24 isprovided in the tank 21. The opening is adapted to enable the casing 12of the particle filter to be connected to it via its open end 16. Thus,the upstream face 14 of the particle filter is exposed facing the insideof the tank 21.

For the purpose of regenerating the soot on the upstream face 14 of theparticle filter, the air taken from the outside by the fan 22 is fedinto the tank and is caused to flow through the particle filter afterhaving been heated in contact with the flame generated by the burner 23.Thus, a stream of hot air is established through the filter from itsupstream face 14 towards its downstream face 18. The stream of hot airis removed via the outlet 20 of the filter.

The fan 22 is adapted for an air flow rate of about 250 kg/h at apressure lying in the range 1 bar to 2 bars. The burner 23 isdimensioned so that the temperature of the gases on the upstream face ofthe particle filter lies in the range 550° C. to 650° C., and, inparticular, less than 600° C.

The stream of hot air through the particle filter is sustained for alapse of time lying in the range 2 minutes to 20 minutes, and preferably5 minutes to 10 minutes.

The flow of hot air through the filter increases the temperature of thesoot present on the upstream face, causing said soot to burn.

After full combustion of the soot, the casing 12 containing the particlefilter 10 is dismounted from the tank 21.

The unburnt residue deposited on the upstream face of the particlefilter 10 is then removed in the facility shown in FIG. 2.

The facility for cleaning the particle filter 10 includes cleaning fluidfeed means 25. Said feed means comprise a reservoir 26 constituted, forexample, by a tank containing water. Water heating means 28 of anysuitable type are installed in the tank 26. The outlet of the tank 26 isconnected to a pump 30 advantageously constituted by a reciprocatingpump. The outlet of the pump is connected to a duct 32 adapted to conveythe stream of cleaning liquid from the reservoir 26 to the outlet of theparticle filter. At its end, the duct 32 has a coupling 34 making itpossible to connect the duct directly and in leaktight manner to theoutlet 20 of the particle filter.

The duct 32 and its coupling 34 are of cross-section substantiallyidentical to the cross-section of the outlet 20.

In addition, a stop valve 36 is provided at the outlet of the pump 30.

Air feed means 38 for feeding in air under pressure are also connectedto the duct 32, downstream from the valve 36.

Said means 38 comprise an air compressor 40 whose outlet is connected toa variable-pressure air tank 42, the pressure of the air in the tanklying in the range 2 bars to 6 bars.

A pressure regulator 44 is interposed between the outlet of thecompressor and the inlet of the tank 42.

The outlet of the tank 42 is connected to the duct 32 via a stop valve46.

The valves 36 and 46 are connected to control means so as to connect theduct 32 alternately to the water feed means 25 or to the air feed means38.

After the regeneration stage performed in the equipment shown in FIG. 1,the outlet 20 of the filter is connected to the duct 32, as shown inFIG. 2. A stream of cleaning liquid (advantageously water) is thencaused to flow through the particle filter 10 from its downstreamsurface 18 towards its upstream surface 14.

The stream of liquid is caused to flow through the filter at a flow rategreater than 50 l/min, the pump 30 being adapted for such a flow rate.Advantageously, said flow rate lies in the range 200 l/min to 600 l/min.It is preferably substantially equal to 300 l/min.

The stream of liquid is distributed over substantially all of thedownstream surface 18 of the particle filter, the volume between thedownstream face 18 and the outlet 20 of the filter being entirely filledwith liquid.

When the stream of liquid is caused to flow, the pressure of the liquid,upstream from the downstream surface 18 of the particle filteradvantageously lies in the range 5 bars to 50 bars. Said pressure ispreferably equal to 20 bars. The pump 20 is adapted to impose such apressure.

The liquid used for sweeping through the particle filter is water,advantageously heated to a temperature lying in the range 30° C. to 70°C. Preferably, said temperature is substantially equal to 50° C.

In the embodiment shown, the water comes from the reservoir 26 equippedwith heater means 28. However, the water may come from a running watersupply network, and in particular from a mixer for mixing hot and coldwater coming from two distinct water supply networks for supplying waterat different temperatures.

A first step in causing the cleaning liquid to flow is performed whilethe upstream face 14 of the particle filter is left free. This firststep lasts for 20 seconds, for example. During this step, the stream ofliquid is maintained continuously with a flow rate and a pressure asindicated above.

Advantageously, during this step, the flow of cleaning liquid isinterrupted by means of the valve 36 shown in FIG. 2. The valve 46 isthen opened. From the air feed means 38, a stream of air is establishedthrough the particle filter 10 from its downstream face 18 towards itsupstream face 14. This second step lasts for 5 seconds, for example.

The blower means 60 are adapted to deliver a stream of air having a flowrate lying in the range 50 l/s to 300 l/s and preferably substantiallyequal to 150 l/s. The pressure upstream from the downstream surface 18of the particle filter lies in the range 2 bars to 10 bars, and isadvantageously substantially equal to 5 bars.

A succession of steps in which the filter is swept through with waterand with air is then implemented. One water sweeping step and one airsweeping step form one cleaning cycle.

One cycle of the cleaning method of the invention advantageously lastsin the range 30 seconds to 50 seconds, and preferably 40 seconds.

Advantageously, for cleaning any one filter, a cleaning cycle isrepeated in the range once to 10 times, and preferably about 5 times.

Advantageously, an additional cleaning step such as the step shown inFIG. 3 is implemented. During this step, the streams of liquid or of gasare sustained under same conditions as above. However, closure means 50,e.g. constituted by a flat disk, are applied against a portion of theupstream surface 14 of the particle filter. The closure means 50 arecarried, for example, by a cross-piece 52 allowing the streams to flowpast on either side of the closure means.

Advantageously, the closure means 50 are placed only in alignment withthe outlet 20 through which the cleaning flows are fed in. Inparticular, the closure means are advantageously mounted in the centralportion of the upstream surface 14 of the particle filter.

This additional step lasts 20 seconds, for example.

After the various cleaning steps, the particle filter is mounted back onthe vehicle.

It can be understood that water and optionally air flowing at highflow-rates and pressures through the particle filter causes thenon-combustible residue deposited on the upstream surface 14 of theparticle filter to be detached and removed. In particular, suchdetaching takes place preferentially in alignment with the outlet 20 viawhich the cleaning liquid is fed in.

During the additional step shown in FIG. 3, the presence of the closuremeans 50 causes the liquid to flow preferentially at the periphery ofthe central region of the filter aligned with the outlet 20. Thus, theregions of the upstream surface 14 of the particle filter that are notcovered by the closure means 50 are then rid of the non-combustibleresidue, since substantially all of the stream of liquid then passesthrough these regions of the upstream surface.

This additional step is preferably implemented. However, it may beomitted.

It is observed that, during the various stages, the high flow-rate ofliquid established through the particle filter, associated with a highpressure of said liquid, guarantees that the residue is detached andremoved satisfactorily. In addition, the higher-than-ambient temperatureof the liquid facilitates the detaching.

In addition, advantageously, before causing the cleaning liquid to flowthrough the particle filter, said particle filter is, after it has beendismounted, immersed with its casing 12 in a bath subjected toultrasound vibration.

1. A method of cleaning the upstream face of a particle filter of an engine exhaust pipe line, the filter being disposed in a casing having an outlet for the exhaust gases, the method comprising a step in which a cleaning stream of liquid is caused to flow back through the particle filter from its downstream face towards its face that is upstream relative to the direction in which the exhaust gases flow through the filter, wherein the cleaning stream of liquid that is caused to flow back through the particle filter is distributed over all of the downstream surface of the particle filter, and wherein the volume between said downstream surface and said outlet is entirely filled with liquid.
 2. A method according to claim 1, wherein the cleaning stream is a stream of liquid whose flow rate is greater than 50 l/min.
 3. A method according to claim 2, wherein the stream of liquid caused to flow through the particle filter has a flow rate lying in the range 200 l/min. to 600 l/min.
 4. A method according to claim 2, wherein the pressure of the liquid upstream from the downstream surface of the particle filter lies in the range 5 bars to 50 bars, and preferably in the range 15 bars to 25 bars.
 5. A method according to claim 1, wherein the liquid has a temperature lying in the range 30° C. to 70° C.
 6. A method according to claim 2, wherein the liquid is water.
 7. A method according to claim 1, further comprising, prior to said step in which a cleaning stream is caused to flow through the particle filter, a step in which the particle filter is immersed in a bath subjected to ultrasound vibration.
 8. A method according to claim 2, further comprising, after the step in which a stream of liquid is caused to flow through the particle filter, a step in which a stream of gas is caused to flow through the particle filter, from its downstream surface towards its upstream surface.
 9. A method according to claim 8, wherein, during the step in which a stream of gas is caused to flow through the particle filter, the stream of gas is distributed over substantially all of the downstream surface of the particle filter.
 10. A method according to claim 8, wherein, during the step in which a stream of gas is caused to flow through the particle filter, the stream of gas has a flow rate greater than 3000 l/min, and a static pressure greater than 2 bars.
 11. A method according to claim 8, comprising a succession of alternating steps in which a stream of liquid is caused to flow through the particle filter and in which a stream of gas is caused to flow through the particle filter, from its downstream surface to its upstream surface.
 12. A method according to claim 1, wherein the cleaning flow is fed into said casing via a duct connected to the outlet via which the exhaust gases exit from the casing, and wherein the cross-section of the duct is substantially equal to the cross-section of the exhaust gas outlet of the casing.
 13. A method according to claim 1, wherein, during a portion of said step in which a cleaning stream is caused to flow through the particle filter, closure means are applied to a small portion of the upstream face of the particle filter.
 14. A method according to claim 1, wherein the particle filter has a plurality of parallel passages therethrough, and wherein said stream of liquid is introduced into the particle filter in a direction parallel to said passages.
 15. A method according to claim 14, wherein said stream of liquid is introduced along a line which is directed centrally of said passages. 